Applicability

User Agent and Assistive Technology Support Notes

There is no universal standard format for representing captions in SMIL 1.0.
Different user agents support different caption formats. A file in a
supported format must be provided as the textstream src argument for the
caption textstream.

QuickTime supports QTText caption files. Real-based players, such as
RealPlayer and GRiNS, support RealText caption files. WindowsMedia supports
SAMI files, but does not support SMIL. Flash does not support a specific file type, but can parse XML-based caption file; actually the FLVPlayback component support for SMIL is intended to detect parameters like movie/server url or multi-bandwidth indications specified in a <switch> tag.

Description

The objective of this technique is to provide a way for people who are deaf
or otherwise have trouble hearing the dialog in audio visual material to be
able to view the material. With this technique all of the dialog and
important sounds are available in a text stream that is displayed in a
caption area.

With SMIL 1.0, separate regions can be defined for the video and the
captions. The captions and video playback are synchronized, with the caption
text displayed in one region of the screen, while the corresponding video is
displayed in another region.

The example shows a <par> segment
containing a <video> and a
<code><![CDATA[<textstream> tag. The system-captions attribute indicates that the
textstream should be displayed when the user's player setting for
captions indicates the preference for captions to be displayed. The
<layout> section defines the regions
used for the video and the captions.